This invention relates generally to ice cube making apparatus and more specifically to an evaporator plate for use in an ice cube making machine.
For the purpose of making cube ice for commercial installations, such as restaurants, bars, motels and the like there are a number of varieties of cube ice machines available on the market. They all include some type of chilled plate or mold in or against which water is delivered for freezing into ice cubes. The chilled member, which supplies the cooling for freezing the water, may be termed an evaporator plate, which conventionally includes refrigerant coils disposed on one side of the plate and on the reverse side some sort of pockets or recesses in which the water is frozen into cubes of ice. In some machines the evaporator plate is disposed horizontally and on some occasions in a vertical position. Whichever disposition is utilized, the evaporator plate must be designed so that water may be delivered to the plate for freezing into cubes and the frozen cubes may thereafter be removed from the plate, or harvested, as such removal is termed.
In order to facilitate harvesting the ice, it is more convenient to position the evaporator plate in a vertical position or a horizontal position with the ice forming molds facing downwardly so that the cubes may be largely harvested by gravity. Examples of ice cube makers having gravity harvesting of the cubes are shown in the U.S. Pats. to Dedricks et al., No. 3,430,452, Johnson, No. 3,913,349, and Dwyer, No. 3,964,270. In the types of machines characterized by the Dedricks et al. patent and the Johnson patent, the evaporator plates are either in a vertical or near vertical position with the cube forming molds being provided by lattice configurations positioned on the evaporator plates on the side remote from the refrigerant coils. Water delivered across the top of the lattice structure runs downwardly across the face of the evaporator plate with portions thereof freezing in the pockets of the lattice as the water trickles across the plate. In the case of the Dedricks et al. patented structure, horizontally extending walls of the lattice are angled downwardly slightly so that the cubes may be harvested by gravity when released from the evaporator plate. Similarly, in the structure disclosed in the Johnson patent, the evaporator plates are tilted downwardly from the vertical so that the horizontal walls of the lattice are tilted downwardly, again, to permit gravity harvesting of the cubes. There are also similar commercial ice machines in which the evaporator plates are positioned vertically but which utilize mechanical harvesting means to disengage the cubes from a lattice work which is not inclined to permit the gravity harvest.
In all these machines utilizing the lattice form molds on generally vertically disposed evaporator plates, the ice making cycle is completed only when a complete slab is formed wherein the pockets in the lattice are full of ice and there are bridging connections between the adjacent rows of cubes to form a continuous slab in which all of the cubes are interconnected. The formation of a continuous slab is important since it facilitates the removal or harvesting of all of the cubes substantially simultaneously. If the cubes were not all connected in a single slab, minor variations in the temperature and the surface texture of the plate or the lattice would result in the cubes being harvested in a random manner with many of the cubes taking longer than average to be disengaged from the evaporator plate and the lattice. Such a random delivery of the cubes would necessitate lengthening the time for the harvesting portion of the cycle and would, therefore, cut down substantially on the output of the machine. Accordingly, one of the main goals in ice machines of this general type is to form a proper slab of ice which is uniform across its face so that it may be harvested to produce maximum output from the machine. If the slab is not uniform in thickness, the bridging portions of ice will be weak in some areas having a tendency to break and thereby retard or prevent the rapid harvesting of all of the ice on the evaporator plate. It should also be noted that if the freezing cycle is extended sufficiently to build up sufficiently strong bridging portions in spite of the uneven freezing across the surface of the slab, the bridging portions in some areas will be very thick. It is well known that an ice machine is operating least efficiently during this terminal portion of the cycle when the water being frozen is insulated from the evaporator plate by a maximum thickness of ice. Therefore, it is important to the efficiency of the ice making machine that the cycle be terminated as soon as possible after the ice has built up over all of the conducting portions of the evaporator plate and its lattice structure.
In considering the refrigeration means associated with the evaporator plate in a typical ice machine, we have noted that the evaporator plate typically includes a coil secured to one side thereof through which the liquid refrigerant is passed. This coil typically takes the form of a copper tube which has a plurality of parallel horizontally disposed legs which traverse the rear face of the evaporator plate and are interconnected by radiused portions of tubing. A refrigerant supply line typically extends from a compressor through a condenser which may be air or water cooled and then through an expansion valve to an input leg at the bottom of the evaporator plate. The liquid refrigerant then traverses the plate through the serpentine coil, passing back and forth through the adjacent horizontal legs in moving to the uppermost leg which is connected to the input of the compressor.
This typical arrangement of the evaporator coil on the plate presents serious drawbacks in the cube ice maker of the types described above. The liquid refrigerant passing through the serpentine coil has various degrees of effectiveness throughout its travel across the plate. When the refrigerant initially enters the evaporator coil, it is characterized by low temperature but has a high velocity which lessens its heat transfer to the plate. By about the midpoint of the serpentine coil, the velocity of the liquid has decreased while the temperature is still low, giving the maximum heat transfer. Thereafter, the liquid warms slightly with there being some gas present toward the output end of the serpentine coil. This diminished effectiveness of the refrigerant as it moves toward the top of the evaporator plate causes the cooling effect to be less which also results in a slower formation of ice at the upper edge of the lattice on the evaporator plate. It should also be noted that the water delivered to the upper edge of the plate is slightly warmer thereby placing a greater load on the refrigerant system at the upper edge of the evaporator plate. This results in slower freezing of the water and thinner bridging members between the ice cubes in the top rows of cubes than is found in other portions of the finished slab of ice. This nonuniformity creates the problems discussed above insofar as harvesting of the ice and efficiency of production are concerned.
When the freezing cycle is completed and harvesting is begun, a solenoid valve in the refrigerant system is actuated, causing hot gas to be delivered to the evaporator coil instead of liquid refrigerant delivered during the freezing cycle. The hot gas quickly raises the temperature of the evaporator plate and the tubing as well as the lattice, causing the slab along with the cubes to be detached from the surfaces on which they were frozen. The harvesting may not take place immediately since there is a thin film of water between the ice and the evaporator plate including the lattice structure, which tends to retain the slab against the evaporator plate as a consequence of the capillary forces involved.
The lattice is provided with drain holes so that as a slab moves slightly away from the evaporator plate, the water causing the capillary forces drains out from between the ice and the evaporator plate. Once the water has been drained, the slab may be harvested quickly and easily either by gravity or other means depending upon the type of machine involved. One of the difficulties involved in this type of harvesting is the fact that the hot gas enters the bottom of the serpentine coil on the evaporator plate causing the greatest melting at the lower edge while the hot gases are relatively cool by the time they reach the outlet on the upper edge of the plate. This differential in gas temperatures results in substantially greater melting of the ice at the bottom than at the top and results in needless wastage of ice prior to the release of the cubes at the top edge of the evaporator plate. In order to obtain maximum efficiency from an ice machine, it is important that a minimum amount of the previously frozen ice be melted during the harvesting portion of the cycle. Ideally the separation of the cubes from the evaporator plate should occur simultaneously across the entire slab to achieve maximum efficiency.